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Biology
Cell Division
and Fertilization
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5 minutes to write your Journal Entry
*participation grade*
Why do we need to replace cells? When has
your body ever needed to replace cells?
How do you think this happens?
Show me your paragraph when you are
finished
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Interphase
Prophase
Metaphase
Anaphase
Telophase
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Facts
• 30,000 -40,000 skin cells die every hour
• In 1 day you lose a million skin cells
• The dust in your house….made mostly of
dead skin cells
• In 1 year, you lose 8 pounds of skin cells
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• Some white blood cells only live a few
hours
• Red blood cells have a life span of 120
days
• Nerve/brain cells live as long as you
do…which why its important you don’t kill
them(example: with drugs) because they
don’t come back!
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How many cells?
An adult human is made up of about 100 trillion cells.
That’s 100 000 000 000 000 cells!
Everyone started out as just one single cell.
How does one cell become 100 trillion?
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Mitosis – Cell Division
This animation will be
explained in more detail
in the slides to come.
For now, just sit back
and watch it.
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Mitosis
Why is mitosis important?
For growth –
How else would you go
from being a single
fertilized egg cell to the
young person you are
today?
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To replace worn/ damaged cells –
- did you know that we shed our skin cells
about every 35 days. But don't worry, we do
not shed all our skin cells at the same time like
snakes do. In human beings, only the skin
cells that are old are shed, others are not.
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To repair damaged tissue
-when you cut yourself,
new skin cells will grow
to seal the wound.
These new cells come
from preexisting cells
found near the wound
that divided many, many
times.
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Cell division and genetic information
Cells don’t just split in half when they
divide. If they did, there wouldn’t
be much of the cells left!
It is essential that the genetic
information carried in a cell
is transferred to the new cells.
Where is genetic information
carried in a cell?
When a cell divides, how can this genetic information
be transferred without any of it being lost?
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Cell division and chromosomes
Chromosomes (parts of DNA) in
the nucleus carry the genetic info
Chromosomes must be accurately
copied and passed on during
cell division.
This is important to make sure
that no genetic information is lost.
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What is mitosis?
Mitosis begins with 1 cell. How
many chromosomes does this
cell contain?
(answer: 4)
original
cell
First the cell makes a copy
of each chromosome…
…then it divides.
new cell has full set of
chromosomes and is
identical to the original
cell.
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cell
division
2 new cells
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What is mitosis?
Each new cell can keep on
dividing by mitosis.
Mitosis makes new cells by
dividing them for growth and
repair in all living things. That’s
how you get
from one cell to 50 billion!
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So what is the life cycle of a
cell?
Think about humans, can
humans reproduce at birth?
What has to happen first?
Lets watch an animation that
shows the cell cycle
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Mitosis animation
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In foldable: write definition and detailed
picture under flap
At the end of Interphase, a cell that is ready
to divide looks like this:
Loosely
coiled DNA
The cell has grown to nearly 2X its original size, and the
DNA has been copied.
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The actual process of dividing is
called : Mitosis
There are 4 main stages:
Prophase
Metaphase
Anaphase
Telophase
To remember order: Pass Me A Taco
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Prophase
Prophase
- Nucleus goes away
- The loosely coiled DNA
condenses (gets supercoiled)forms chromosomes. You see
chromosomes (like the letter “X”)
in a microscope
- Centrioles release spindle fibres;
spindle fibers will attach to the
centromere of each chromosome
- by the end of prophase, the
nuclear membrane is completely
gone
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Metaphase
• chromosomes move to
middle of the cell
• spindle fibers, attached to
the centromere of each
chromosome, help the
chromosomes move to
the middle
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Anaphase
• Each chromosome
separates so that a
copy of each DNA
molecule moves to
the poles of the cell
• Chromosomes pulled
apart
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Telophase
• The spindle fibers disappear
• A nucleus reforms
• The cell begins to pinch apart at
the centre until it completely
separates into 2 distinct cells, each
with its own set of genetic material
(DNA). This division of the
cytoplasm is called cytokinesis.
Cell organelles are also equally
distributed between the daughter
cells
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Mitosis makes identical cells!!!
They are clones!
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Mitosis animation
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Mitosis summary
How does mitosis turn one cell into two new cells?
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What phase is this?
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What phase is this?
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What phase is this?
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What phase is this?
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What phase is this?
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What phase is this?
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What phase is this?
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What phase is this?
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What phase is this?
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